The review article describes the interplay of fundamental research and advanced processes that have made SiC a unique semiconductor material for power electronic devices. Related to the outstanding physical properties of SiC, the preparation of this material is quite challenging. Processing is carried out at elevated temperatures that require special emphasis on the design of the growth machine and the applied construction materials. Growth inside a closed growth chamber demands the usage of advanced sensors and sophisticated computer simulation of the growth process. The application of advanced 2D and 3D in situ x-ray visualization techniques enables the visualization of the growth process. Reduction of the density of structural defects, a prerequisite for the technical application in power electronic devices, based on fundamental research and understanding of the crystallographic as well as the electronic properties of SiC beyond the knowledge base of standard semiconductor materials.

https://iopscience.iop.org/article/10.1088/1361-6641/aad831/pdf

Review of SiC crystal growth technology

We investigate the optical properties of two sets of Si-doped GaN epitaxial layers with different degree of compensation. The electron concentration dependence of the band-gap energy measured by photoluminescence is interpreted as band-gap narrowing effect and evaluated by a simple relation. The photoluminescence peak positions of heavily compensated samples are shifted downward with respect to those of moderately compensated samples, and the down shift becomes larger at higher electron density. Based on analysis of photoluminescence spectra, these prominent behaviors are accounted for by band-edge potential fluctuation associated with inhomogeneous residual impurities.

Band-gap narrowing and potential fluctuation in Si-doped GaN

Short-period superlattices consisting of alternating layers of GaN:Mg and AlGaN:Mg were grown by low-pressure organometallic vapor phase epitaxy. The electrical properties of these superlattices were measured as a function of temperature and compared to conventional AlGaN:Mg layers. It is shown that the optical absorption edge can be shifted to shorter wavelengths while lowering the acceptor ionization energy by using short-period superlattice structures instead of bulk-like AlGaN:Mg.

Aluminum gallium nitride short-period superlattices doped with magnesium

The low residual doping of HTCVD grown semi-insulating SiC crystals enables the use of decreased concentrations of compensating deep levels, thereby providing new material solutions for microwave devices. Depending on the growth conditions, high resistivity crystals with either a dominating Si-vacancy absorption or with an EPR signature of intrinsic defects such as the C-vacancy and the Si-antisite are obtained. The electrical properties of substrates with resistivities above 10(11) Omega-cm are shown to be stable upon annealing during SiC epitaxy conditions. Micropipe closing at the initial growth stage enables the demonstration of low defect density off- and on-axis 2 2-inch semi-insulating 4H SiC substrates with micropipe densities down to 1.2 cm(-2).

HTCVD grown semi-insulating SiC substrates

A theoretical framework that provides a quantitative relationship between point defect formation energies and growth process parameters is presented. It enables systematic point defect reduction by chemical potential control in metalorganic chemical vapor deposition (MOCVD) of III-nitrides. Experimental corroboration is provided by a case study of C incorporation in GaN. The theoretical model is shown to be successful in providing quantitative predictions of CN defect incorporation in GaN as a function of growth parameters and provides valuable insights into boundary phases and other impurity chemical reactions. The metal supersaturation is found to be the primary factor in determining the chemical potential of III/N and consequently incorporation or formation of point defects which involves exchange of III or N atoms with the reservoir. The framework is general and may be extended to other defect systems in (Al)GaN. The utility of equilibrium formalism typically employed in density functional theory in p...

Point defect reduction in MOCVD (Al)GaN by chemical potential control and a comprehensive model of C incorporation in GaN

Vanadium-free Semi-insulating 4H-SiC Substrates

Photo-Electron Paramagnetic Resonance (photo-EPR) measurements of semi-insulating (s.-i.) 4H SiC have been made at 37 GHz including photo excitation and photo quenching techniques in the temperature interval from 77 K to 50 K. At T = 77 K in the dark the EPR spectrum consists of a low intensity line due to boron on the cubic lattice site and a single line with isotropic g ∥ = g ⊥ = 2.0025 due to a carbon-related surface defect. During illumination with ultraviolet light the EPR lines of hexagonal boron and cubic nitrogen appear in the EPR spectrum and persist after the illumination is removed. Subsequent illumination of the sample with sub-band gap, visible, light resulted in the quenching of the EPR lines from nitrogen and appearance of the I P1 EPR line with g ∥ = 2.0048, g ⊥ = 2.0030 caused by direct transfer of electrons from nitrogen donor to the P1 center. The lifetime of the photo-generated carriers trapped by the P1 centers is found to be more than 15- 20 hours after the photo-excitation was turned off. The deep donor P1 local center is suggested to be the as yet unidentified deep level located at E C – 1.1 eV which pins the Fermi level in this sample at this energy in the dark. As the temperature is lowered from 77K and the quasi Fermi level positions reach shallow donor and acceptor states, an additional EPR line, I D , with g ∥ = 2.0063, g ⊥ = 2.0006, appears at 50 K in the excitation EPR spectrum and is attributed to the antisite defect Si − c with an energy level shallower than nitrogen. At the same time the ratio of the photo-excited EPR line intensities responsible for boron on the cubic and hexagonal sites, I k B :I h B , returns to the value observed at 77 K and becomes equal to 0.4 at 50 K, showing that the concentration of boron in the hexagonal site is higher than on the cubic site.

Photo EPR Study of Trapping and Recombination Processes in Semi-Insulating 4H-SiC Crystals as Function of Temperature

GaN films grown by low-pressure metalorganic chemical vapor deposition using trimethylgallium and triethylgallium as gallium precursors are compared. The films were characterized by x-ray diffraction, Hall effect, photoluminescence, secondary ion mass spectroscopy, and etch pit density measurements. GaN layers grown using triethylgallium exhibited superior electrical and optical properties and a lower carbon impurity concentration.

/pdf/comparison-of-trimethylgallium-and-triethylgallium-for-the-3j77zjeb68.pdf

Comparison of trimethylgallium and triethylgallium for the growth of GaN

GaN Doped with Sulfur

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Vanadium-free Semi-insulating 4H-SiC Substrates

Photo EPR Study of Trapping and Recombination Processes in Semi-Insulating 4H-SiC Crystals as Function of Temperature

Comparison of trimethylgallium and triethylgallium for the growth of GaN

GaN Doped with Sulfur